Originally Posted by Cab_Burge
I saw witness marks on all the outer edges of my old pump gas motor pistons at .035, none after changing it to .040+ up
The ring lands where fine, no damage but the edges where shiny, no carbon and the same marks on the heads work
that motor got shifted at or above 7000 RPM on every run also so shruggy

Mine's been good with .040", even with some piston-to-bore clearances looser than I'd prefer. I wouldn't feel comfortable with much less, having seem other engines with witness marks like Cab mentioned when running a tad too close.